A fine substance having a size in the order of nanometer, such as a nanotube, a fullerene, a nanowire and a nanosheet has a novel property which cannot be expressed in a bulk state, and its application has been expected in a variety of fields.
For example, concerning with a carbon nanotube, its application to a flat display panel or the like has been progressed as an excellent electron discharging material and its application to a fuel electric cell or the like as a storage source of hydrogen has also been studied as well. Moreover, a carbon nanotube has also been expected as a wiring material that can realize a superfine wiring which is difficult to be performed by a conventional process of processing a wiring.
A nanowire made of metal (hereinafter, referred to as a metal nanowire) has also been expected to be applied as a wiring material in the same manner as a carbon nanotube, and it has also been considered to be applied to a magnetic memory medium or a magnetic memory element and to be utilized as a catalyst as well. However, regarding a metal nanowire whose aspect ratio (ratio of the length with respect to the diameter=the length/the diameter) is small, there have been many reports of manufacturing examples at a laboratory level, however, manufacturing a metal nanotube with a high aspect ratio, whose utilization value is larger, is difficult.
As a process for manufacturing a metal nanotube whose aspect ratio is large, electrolytic deposition using a template has been disclosed, for example, in G. Tourillon et al., “Electrochemically Synthesized Co and Fe Nanowires and Nanotubes” (Electrochemical and Solid-State Letters, The Electrochemical Society, Inc., January 2000, Vol. 3, No. 1, p. 20 to 23, hereinafter, referred to as G. Tourillon et al.). In the process of G. Tourillon et al., a polycarbonate film with a thickness of 6 μm which has a large number of penetrated holes having a diameter of 30 nm is utilized as a template, a layer composed of Au is formed on the surface of this polycarbonate film as a cathode by a classical vapor deposition process, the space between the cathode and the anode is filled with an electrolyte solution comprising 0.1M CoSO4 or FeSO4 and 0.1M H3BO3, and a periodic functional voltage consisting of the two stages of a rectangular wave at −1.5 V for 0.3 to 0.5 second as the first stage and a rectangular wave at −0.9 V for 2 seconds as the second stage is serially applied. Co or Fe is precipitated on the wall surface of the penetrated hole of the polycarbonate film and a nanowire comprising Co or Fe can be obtained. Moreover, it has been reported that the operation, wherein a periodic waveform was continued to be applied for 8 minutes in which a pulse voltage at −1.5 V for 0.1 second was applied at the first stage after the waveform was changed and then the current was cut off for 2 seconds at the second stage, was carried out, and as a result, a nanotube comprising Co was formed. In G. Tourillon et al., the mechanism of forming a nanotube is considered such that a metal nanotube is formed by the first stage mechanism of capturing metal ions to the wall surface of the carbonate film due to a complex of carbonate (CO32− group) of the carbonate film and metal ions (Fe2+ and Co2+) in the electrolyte solution to be formed and by the subsequent second stage mechanism of reducing reaction of metal ions. In the case where the electrocrystallization continuation time exceeds over 20 to 22 minutes, the inner side of the tube is embedded with metal clusters to form a nanowire.
Moreover, since the layer made of Au which is to be an electrode is formed on the bottom surface of the polycarbonate film by a classical vapor deposition process, it is estimated that the thickness of the metal layer is not less than 200 nm, as well as the thin film is considerably ununiform, and therefore it is extremely highly possible that the surface of the polycarbonate film is not uniformly covered by the coating of Au. In G. Tourillon et al., it has been described that the metal layer formed by an electrolysis grows in the direction towards the inner side from the wall surface of a nanotube and a cluster is generated in the inner side of a nanotube. Then, since a process for forming a metal layer trace by trace utilizing a pulse voltage is employed, in order to obtain Co and Fe tubes whose wall thickness is only 1 to 2 nm, it requires 15 minutes when the metal ion capturing stage and the metal ion reducing stage are totaled.
Moreover, an example of manufacturing a nanowire and a nanotube composed of Ni has been disclosed in Jianchun Bao et al., “Template Synthesis of an Array of Nickel Nanotubules and Its Magnetic Behavior” (Advanced Materials, WILEY-VCH Verlag GmbH, November 2000, Vol. 13, No. 21, p. 1631 to 1633, hereinafter referred to as Jianchun Bao et al.). In Jianchun Bao et al., a porous film composed of alumina is used as a template, after this alumina porous film has been treated with an organic amine, an electrocrystallization is performed at a current density of 0.3 mA/cm2 for 24 hours, and a Ni nanotube having a diameter of 160 nm, a length of 20 μm and a wall thickness of 30 nm was obtained. Moreover, an electrocrystallization was performed for 48 hours under the same conditions, and Ni nanotube having a diameter of 160 nm, a length of 35 μm and a wall thickness of 60 nm was obtained.
However, in Jianchun Bao et al., in order to obtain a nanotube having a length of 20 μm, it required 24 hours for electrolysis time, thus being inefficient.
An object of the present invention is to provide an apparatus with which a high quality metal nanotube can be manufactured in a short time and a process for manufacturing the same.